As disclosed in Japanese Utility Model Laid-Open Nos. 2-6291 and 2-107089, a conventional wristwatch with a vibration alarm as an electronic equipment for generating vibration by rotating an eccentric weight by a motor incorporates an ultrasonic motor. The rotation of the rotor of the ultrasonic motor is transmitted to an eccentric weight wheel having an eccentric barycentric position. Vibration caused by the rotation of the eccentric weight wheel is transmitted to the user's arm through the watch case, thereby alarming the user by a vibration alarm.
In the ultrasonic motor of the Japanese Utility Model Laid-Open Nos. 2-6291 and 2-107089, a vibrator bonded with a piezoelectric element is supported by a support pin, and the rotor and the vibrator are brought into tight contact with each other by a compression spring. The operational principle of the ultrasonic motor is to deflect and enlarge the vibration of the piezoelectric element by a comb gear portion provided to the vibrator, to generate a traveling wave in the comb gear portion, and to rotate the rotor by a frictional compression force of the comb gear portion and the rotor.
More specifically, the rotor is rotated while it is constantly urged against the comb gear portion of the vibrator by the compression spring. Then, wear of the contact portion of the rotor and the comb gear portion is unavoidable, providing insufficient durability.
Since the vibration of the piezoelectric element has a small amplitude, the comb gear portion of the vibrator for deflecting and enlarging this amplitude requires especially high machining precision. Hence, it is difficult to machine the comb gear portion of the vibrator. In order to stably rotate the rotor, not only the vibrator but also other components, e.g., the piezoelectric element and the rotor must have high machining precision and high assembling precision.
It is an object of the present invention to provide a reliable small electronic equipment with a vibration alarm (e.g., a wristwatch), which has a rotor having high rotational durability, can be assembled easily, has low power consumption, can be stably started even if an acceleration is applied to it when, e.g., the user swings his arm, and has a stepping motor as a drive source in order to enable high-speed rotation.